Ultrasonic Evaluation of Cervical Length in Pregnancies Complicated by Preterm Premature Rupture of the Membranes 

Abstract & Commentary

Gire and colleagues recently published data that have interesting potential in the management of patients with preterm premature rupture of the membranes (PPROM). Over a 3-year period they assessed cervical lengths through transvaginal ultrasound examinations on admission in more than 100 patients diagnosed with PPROM. Gire et al were interested in determining if cervical length was related to the development of chorioamnionitis in these patients, who, by protocol, were managed expectantly unless there was evidence of infection. Although there was no statistically significant relationship between cervical length and maternal or neonatal sepsis, there was a strong relationship between cervical length and length of latency. Using a receiver operator curve (ROC) Gire et al found, using a 2 cm cutoff, that the average time from admission to delivery was 59 hours when cervical length was below this threshold, compared with 240 hours when cervical length was longer than 2 cm. There was a trend toward a higher rate of chorioamnionitis in multiparas who presented after 28 weeks with longer cervices, but this was not statistically significant (Gire C, et al. Ultrasound Obstet Gynecol. 2002;19[6]:565-569).

Comment by John C. Hobbins, MD

PPROM occurs in about 3% of pregnancies but is responsible for substantial perinatal morbidity secondary to prematurity and/or maternal or neonatal sepsis. In PPROM, a good noninvasive predictor of chorioamnionitis is yet to be found. However, this study helps to distinguish patients who will deliver within a few days of admission from those who will be in the hospital for at least 10 days.

Some have questioned the safety of transvaginal ultrasound examination in premature rupture of the membranes because of the potential to introduce bacteria into the cervix. Upon entering the vagina, the transducer is on course to make contact with the cervix well back in the anterior fornix and far from the exocervix. Also, the transducer would add few new bacteria to the already rich microbial environment in the vagina.

Gire et al found that patients who were more than 28 weeks tended to have a greater chance of chorioamnionitis if their cervices were long is intriguing. On one hand, if a patient is developing chorioamnionitis, one might expect the cervix to be soft and well effaced because of the indirect action on the collagen and elastin of the cervix. However, if membranes are ruptured because of intracervical exposure to bacteria alone, then a long cervix might be expected, as long as it is not coupled with ascending infection, which would come later.

For years physicians have been reluctant to send patients home with PPROM because: a) they often go into labor soon after rupture of the membranes; b) of concern that early signs of infection will go unnoticed; and c) of liability if complications occur.

According to the above study, transvaginal ultrasound should be able to predict which patients would be most likely to occupy a bed for at least a week and a half while being exposed to the hospital’s own special brand of microbes. Often patients would be far happier in their home environment and it would be substantially less expensive to use some form of home surveillance for the right patient, rather than having her "stew" in the hospital for more than 10 days (costing between $1500 and $2000/day by my most recent calculations).

Obviously many safeguards would have to be set up to make sure that early signs of chorioamnionitis would not be missed, and expeditious transfer to the hospital could be accomplished.

Certainly this study presents food for thought.

Dr. Hobbins is Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver.